LED lighting technology is rapidly developing to replace traditional incandescent and fluorescent lightings. LED tube lamps are mercury-free in comparison with fluorescent tube lamps that are filled with inert gas and mercury. Thus, LED tube lamps are becoming an illumination option among different available lighting systems used in homes and workplaces, which used to be dominated by traditional lighting options such as compact fluorescent light bulbs (CFLs) and fluorescent tube lamps. Benefits of LED tube lamps include improved durability and longevity and far less energy consumption; therefore, when taking into account all factors, they are typically considered a cost-effective lighting option.
Typical LED tube lamps each have a variety of LED lamp components and driving circuits. The LED lamp components include LED chip-packaging elements, light diffusion elements, high efficient heat dissipating elements, light reflective boards and light diffusing boards. Heat generated by the LED lamp components and the driving elements is considerable and mainly dominates the illumination intensity such that the heat dissipation needs to be properly disposed to avoid rapid decrease of the luminance and the lifetime of the LED lamps. Thus, power loss, rapid light decay, and short lifetime due to poor heat dissipation tend to be factors to be considered when improving the performance of the LED illuminating system.
Nowadays, most LED tube lamps use plastic tubes and metallic elements to dissipate heat from the LEDs. The metallic elements are usually exposed to the outside of the plastic tubes. This design improves heat dissipation but heightens the risk of electric shocks. The metallic elements may be disposed inside the plastic tubes, however the heat still remains inside the plastic tubes and deforms the plastic tubes. Deformation of the plastic tubes may also occur when the elements to dissipate heat from the LEDs are not metallic.
The metallic elements disposed to dissipate heat from the LEDs may be made of aluminum. However, aluminum is typically too soft to sufficiently support the plastic tubes when the deformation of plastic tubes occurs due to the heat as far as the metallic elements disposed inside the plastic tubes are concerned.
Further, circuit design of current LED tube lamps mostly doesn't provide suitable solutions for complying with relevant certification standards and for better compatibility with the driving structure using an electronic ballast originally for a fluorescent lamp. For example, since there are usually no electronic components in a fluorescent lamp, it's fairly easy for a fluorescent lamp to be certified under EMI (electromagnetic interference) standards and safety standards for lighting equipment as provided by Underwriters Laboratories (UL). However, there are a considerable number of electronic components in an LED tube lamp, and therefore the impacts caused by the layout (structure) of the electronic components is important, resulting in difficulties in complying with such standards.
On current markets there are two ways of replacing current lighting devices, mostly fluorescent lamps, with LED lamps. One way is to use a ballast-compatible LED lamp. In the present disclosure, being ballast-compatible means this type of LED lamp can work with a ballast to emit light. A ballast-compatible LED lamp can receive the high frequency AC signal (generally with a frequency of some tens of kHz) generated by a ballast, in working to emit light. Therefore, an LED lamp tube of the ballast-compatible type can be directly substituted for a traditional fluorescent lamp tube without the need to retrofit the original lamp base or wiring/circuits for the LED lamp. The other way is to use an LED lamp of the ballast-bypass type, which can work to emit light by receiving the low frequency AC signal (generally with a frequency of 50 or 60 Hz) generated by a common AC powerline (also called household power or line power), but not the high frequency AC signal generated by a ballast. Therefore, in these types of lamps, the traditional ballast used with a fluorescent lamp should be removed or bypassed, for directly connecting a common AC powerline to an LED lamp of the ballast-bypass type for using the LED lamp.
LED lamps on current markets are of either the ballast-compatible type or the ballast-bypass type, and the production and management of each are often distinctly handled by their manufacturers. As a result, this situation not only increases burdens and troubles of each type's production and management on the part of their manufacturers, but also causes confusion and hassles to end users on using or installing each type because end users are required to be able to distinguish between them when purchasing/using them. Furthermore, these LED lamps cannot switch to appropriate ones of LED driving modes corresponding to different driving power supplies, and therefore end users cannot tell which of the LED lamp and the current driving power supply to be used together is not usable/compatible with the other. As to emergency lighting, the LED lamp should be supplied by an emergency power supply upon an emergency event (such as a breakoff of the original power supply). But emergency power supplies are usually DC power supplies, and current LED lamps cannot properly work when supplied by a DC power supply.
The driving of an LED uses a DC driving signal, but the driving signal for a fluorescent lamp is a low-frequency, low-voltage AC signal as provided by an AC powerline, a high-frequency, high-voltage AC signal provided by a ballast, or even a DC signal provided by a battery for emergency lighting applications. Since the voltages and frequency spectrums of these types of signals may differ significantly, simply performing a rectification to produce the required DC driving signal in an LED tube lamp is not generally competent at achieving the LED tube lamp's compatibility with traditional driving systems of a fluorescent lamp.
In addition, for some LED tube lamps, a rigid circuit board is typically electrically connected with the lamps' end caps by way of wire bonding, in which the wires may be easily damaged and even broken due to any move during manufacturing, transportation, and usage of the LED tube lamps and therefore may disable the LED tube lamps. Or, a bendable circuit sheet may be used to electrically connect the LED assembly in the lamp tube and the power supply assembly in the end cap(s). The length of the lamp tube during manufacturing may be matched for the bendable circuit sheet, and thus the variable factor increases in the manufacture of the lamp tube.
The heat generated by the LED tube lamp can be reduced through controlling the LED illumination and lighting period by an LED driving circuit. However, it is not easy to meet the expected LED illumination requirement based on some analog driving manners since the relationship between the LED illumination and the LED current is non-linear and color temperature of some LEDs changes according to LED current. Moreover, heat convection in the lamp tube is not easily performed, e.g., in some cases, the lamp tube is even a confined space, and once the LED illumination increases, the life span of the LED tube lamp shortens because the life span of LEDs is sensitive to temperature. Also, some LED driving circuits result in the circuit bandwidth getting smaller since the driving voltage/current repeatedly returns between the maximum and minimum. This may limit the minimum conducting period and affects the driving frequency.
In addition, the LED tube lamp may be provided with power via two ends of the lamp and a user can be easily electrically shocked when one end of the lamp is already inserted into an terminal of a power supply while the other end is held by the user to reach the other terminal of the power supply.
As a result, currently applied techniques often fall short when attempting to address the above-mentioned worse heat conduction, poor heat dissipation, heat deformation, electric shock, weak electrical connection as between the end cap and the lamp tube, smaller driving bandwidth, a lack of appropriate emergency lighting function suitable for emergency driving signal or environment, and variable factors in manufacture defects.